Others have given you a lot of info here on what it is your brother is referring to.
But what this is reflecting in your brother is that he has fallen into a pipeline of watching these videos or hanging out with people that watch these videos and had some insecurities that he's dealing with that is making these ideas seem like the answer. It would be a great idea to be supportive of him in whatever other hobbies/activities he has outside of watching those videos and spending time with him. Talk with him about anything other than the content of those videos so that those thoughts aren't even entering his mind. Introduce him to your friends that are also supportive in something other than those videos (you don't mention your ages, so it's unclear if you know the same people). Having supportive people around his activities and hobbies will help him lose some of those insecurities that made him gravitate to those videos.

If that fails, what I've seen others say works is if says he's an alpha male say back "I'm not into that furry stuff, but that's really cool your so open with your sexuality like that, and accepting of others' sexualities like recognizing the beta males"

[–] [email protected] 3 points 9 hours ago

If that fails, what I’ve seen others say works is if says he’s an alpha male say back “I’m not into that furry stuff, but that’s really cool your so open with your sexuality like that, and accepting of others’ sexualities like recognizing the beta males”

I doubt that actually works to get people off that mindset. It's just a funny twitter joke people have latched onto. Other than that 100% agreed. If he's fallen into this manosphere shit things probably aren't going well for him socially and he probably needs help to get out of it. When I was young I certainly did and was fortunate enough to get into a much better environment after I got out of high school that corrected my mindset (for the most part, there's always a need for self-reflection). While deserved, ridiculing him for these beliefs won't get anywhere other than to make him feel more isolated.